Method and device for deblocking-filtering, and method and device for encoding and decoding using same

ABSTRACT

An encoding apparatus for encoding a video signal includes: a prediction unit for generating a prediction block of a current block by using intra prediction or inter prediction; a residual data encoding unit for generating a residual block by using the current block and the prediction block, and transforming and quantizing the residual block; a residual data decoding unit for decoding a transformed and quantized residual block by inversely quantizing and inversely transforming the transformed and quantized residual block; and a deblocking filter unit for generating a reconstructed block by using a decoded residual block and the prediction block, and performing deblocking filtering, based on inter prediction information and intra prediction information of the reconstructed block and blocks neighboring the reconstructed block. The intra prediction information includes at least one of an intra prediction mode and an intra prediction block size.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 13/811,596 filed Apr. 11, 2013, which is a the National Phaseapplication of International Application No. PCT/KR2011/005359, filed onJul. 20, 2011, which is based upon and claims the benefit of prioritiesfrom Korean Patent Application No. 10-2010-0070180, filed on Jul. 20,2010, No. 10-2011-0022666, filed on Mar. 15, 2011 and No.10-2011-0072071, filed on Jul. 20, 2011. The disclosures of theabove-listed applications are hereby incorporated by reference herein intheir entirety.

TECHNICAL FIELD

The present disclosure in one or more embodiments relates to adeblocking filtering method and apparatus for reducing blocking artifactoccurring in the process of encoding and decoding images, and anencoding and decoding method and apparatus using the same.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

In video encoding, when an image is encoded and then reconstructed inunits of blocks, distortion occurs in block boundaries due to block-unitprediction and quantization. The phenomenon that distortion occurs inblock boundaries is referred to as blocking artifact.

In the existing video encoding standards, such as MPEG-1, MPEG-2, andH.263, a reconstructed image is stored in a reference picture memory,without processing blocking artifact. Therefore, a subjective videoquality of an image is degraded. Furthermore, referencing an imagecontaining blocking artifact during a motion compensation leads to videoquality degradation accumulated in an encoded image. The consequence ofletting an image with the video quality degradation is reduction of theencoding efficiency.

In order to solve these problems, the conventional H.264/AVC attempts tominimize blocking artifact by applying a deblocking filter beforestoring a reconstructed image in a picture memory. In this manner, theconventional H.264/AVC increases a subjective video quality and improvesencoding efficiency through a more accurate signal prediction. However,if deblocking filtering is performed on an image showing no blockingartifact, unnecessary computation increases and unintended video qualitydegradation may unnecessarily occur. Therefore, in order to performdeblocking filtering more effectively, it is necessary to adaptivelyperform different levels of deblocking filtering according to the degreeof blocking artifact.

The H.264/AVC standard adaptively performs the deblocking filteringaccording to the degree of the blocking artifact. That is, a boundarystrength (BS) value for determining filtering strength is determined,and a different level of deblocking filtering is performed according tothe determined BS value. The BS value ranges from 0 to 4. As the BSvalue is larger, it is necessary to perform stronger deblockingfiltering. That is, when the BS value is 0, no deblocking filtering isperformed. When the filtering strength value is 4, the strongestdeblocking filtering is performed.

A deblocking filtering method of the H.264/AVC standard, which is theconventional technology using the deblocking filtering, will bedescribed below in detail.

FIG. 1 shows a block unit and sequence to which deblocking filteringused in the conventional H.264/AVC standard is applied.

The H.264/AVC standard determines the block unit to which deblockingfiltering is applied according to a transform block. That is, if atransform block of 4×4 unit is used, a block to which deblockingfiltering is applied also becomes 4×4 unit. The H.264/AVC standard mayuse a transform block of 8×8 unit, as well as the transform block of 4×4unit. Therefore, if the transform block of 8×8 unit is used, a block towhich deblocking filtering is applied also becomes 8×8 unit. Forconvenience of description, FIG. 1 assumes the case of using thetransform block of 4×4 unit.

Referring to FIG. 1, deblocking filtering is performed on a luma signalblock of 16×16 unit in the orders of vertical directions a, b, c and dof 4×4 unit and horizontal directions e, f, g and h of 4×4 unit. In asimilar manner to the luma signal block, deblocking filtering isperformed on a chroma signal block of 8×8 unit in the orders of verticaldirections i and j of 4×4 unit and horizontal directions k and l of 4×4unit.

FIG. 2 shows pixels p0, p1, p2 and p3 and pixels q0, q1, q2 and q3 ofneighboring blocks P and Q for determining BS, and FIG. 3 shows aprocess of determining a BS in the H.264/AVC standard.

Referring to FIG. 3, it is determined whether the block P or Q shown inFIG. 2 is an intra prediction block (S310). When the block P or Q is theintra prediction block, it is determined whether the pixels p0 and q0are located at a macroblock boundary (S320). When the pixels p0 and q0are located at the macroblock boundary, BS value is 4. On the otherhand, when the pixels p0 and q0 are not located at the macroblockboundary, BS value is 3.

When step S310 determines that both of the blocks P and Q are the intermode, it is determined whether a nonzero transform coefficient ofresidual data exists in the block where the pixel p0 or q0 is located(S330). When the nonzero transform coefficient exists, BS value is 2.

However, when the nonzero transform coefficient does not exist, BS valueis 1 in the case where the pixels p0 and q0 use different referencepictures or have different motion vector values; otherwise, BS value is0 (S340).

That is, in order to selectively remove distortion between blocks, whichis caused by block-unit prediction and quantization, the H.264/AVCstandard selectively uses deblocking filters having different strengths,considering quantization parameter (QP), encoding mode, motioninformation (reference picture, motion vector).

The H.264/AVC standard performs the selective deblocking filtering onthe inter prediction block, additionally considering the motioninformation and the like. However, with respect to the intra predictionblock, the H.264/AVC standard merely references whether the intraprediction block is the boundary of the macroblock, and does not performthe selective deblocking filtering considering the intra predictioninformation. Therefore, in order to perform a further improveddeblocking filtering on the intra prediction block, there is a need fora method that adaptively performs deblocking filtering according tointra prediction information.

DISCLOSURE Technical Problem

Therefore, the present disclosure is directed to improve a subjectivepicture quality and encoding efficiency by adaptively performingdeblocking filtering on an intra prediction block according to intraprediction information.

SUMMARY

An embodiment of the present disclosure provides an encoding apparatusfor encoding a video signal, including: a prediction unit for generatinga prediction block of a current block by using intra prediction or interprediction; a residual data encoding unit for generating a residualblock by using the current block and the prediction block, andtransforming and quantizing the residual block; a residual data decodingunit for decoding a transformed and quantized residual block byinversely quantizing and inversely transforming the transformed andquantized residual block; and a deblocking filter unit for generating areconstructed block by using a decoded residual block and the predictionblock, and performing deblocking filtering, based on inter predictioninformation and intra prediction information of the reconstructed blockand blocks neighboring the reconstructed block.

When the reconstructed block and at least one of the blocks neighboringthe reconstructed block are intra-predicted, the deblocking filter unitmay adaptively determine the filtering strength, based on at least oneof existence/nonexistence of a nonzero transform coefficient exists inthe reconstructed block and at least one of the neighboring blocks,intra prediction information of the reconstructed block and theneighboring blocks, macroblock mode information of the reconstructedblock and the neighboring blocks, and block boundary directions of thereconstructed block and the neighboring blocks.

When the reconstructed block is intra-predicted, the deblocking filterunit may determine the filtering strength, based on at least one ofwhether the nonzero transform coefficient exists in the reconstructedblock and whether the deblocking direction of the reconstructed blockand the intra prediction direction are identical to each other.

The deblocking filter unit may adaptively determine target pixels to befiltered, based on the intra prediction information.

The deblocking filter unit may determine the number of the targetpixels, based on an intra prediction block size included in the intraprediction information.

The deblocking filter unit may determine a filtering direction of thetarget pixels, based on an intra prediction mode included in the intraprediction information.

Another embodiment of the present disclosure provides a decodingapparatus for decoding a video signal, including: a residual datadecoding unit for decoding a transformed and quantized residual blockinput thereto by inversely quantizing and inversely transforming thetransformed and quantized residual block; a prediction unit forgenerating a prediction block, based on inter prediction information orintra prediction information input thereto; and a deblocking filter unitfor generating a reconstructed block by using a decoded residual blockand the prediction block, and performing deblocking filtering, based onthe inter prediction information and the intra prediction information ofthe reconstructed block and blocks neighboring the reconstructed block.

When the reconstructed block and at least one of the blocks neighboringthe reconstructed block are intra-predicted, the deblocking filter unitmay adaptively determine the filtering strength, based on at least oneof existence/nonexistence of a nonzero transform coefficient exists inthe reconstructed block and at least one of the neighboring blocks,intra prediction information of the reconstructed block and theneighboring blocks, macroblock mode information of the reconstructedblock and the neighboring blocks, and block boundary directions of thereconstructed block and the neighboring blocks.

When the reconstructed block is intra-predicted, the deblocking filterunit may determine the filtering strength, based on at least one ofwhether the nonzero transform coefficient exists in the reconstructedblock and whether the deblocking direction of the reconstructed blockand the intra prediction direction are identical to each other.

The deblocking filter unit may adaptively determine target pixels to befiltered, based on the intra prediction information.

The deblocking filter unit may determine the number of the targetpixels, based on an intra prediction block size included in the intraprediction information.

The deblocking filter unit may determine a filtering direction of thetarget pixels, based on an intra prediction mode included in the intraprediction information.

Still another embodiment of the present disclosure provides a deblockingfiltering apparatus that, when at least one of two neighboring blocks isintra-predicted, adaptively determines filtering strength, based on atleast one of existence/nonexistence of a nonzero transform coefficientin at least one of the two neighboring blocks, intra predictioninformation of the two neighboring blocks, macroblock mode informationof the two neighboring blocks, and block boundary directions of the twoneighboring blocks.

Yet another embodiment of the present disclosure provides a deblockingfiltering apparatus that, when a current block is intra-predicted,adaptively determine filtering strength, based on at least one ofwhether a nonzero transform coefficient exists in the current block andwhether a deblocking direction of the current block and an intraprediction direction of the current block are identical to each other.

Yet another embodiment of the present disclosure provides a deblockingfiltering apparatus that, when at least one of two neighboring blocks isintra-predicted, adaptively determines target pixels to be filtered,based on intra prediction information including at least one of an intraprediction mode and an intra prediction block size.

The deblocking filtering apparatus may adaptively determine the numberof the target pixels, based on the intra prediction block size.

The deblocking filtering apparatus may adaptively determine thepositions (filtering direction) of the target pixels, based on the intraprediction mode.

Yet another embodiment of the present disclosure provides an encodingmethod, a decoding method, and a deblocking filtering method that areperformed in the encoding apparatus, the decoding apparatus, and thedeblocking filtering apparatus described above.

ADVANTAGEOUS EFFECTS

According to the present disclosure as described above, a subjectivevideo quality and encoding efficiency can be improved by reducingblocking artifact even with respect to an intra prediction block.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a block unit and sequence to which deblocking filtering isapplied as used in the conventional H.264/AVC standard;

FIG. 2 shows pixels p0, p1, p2 and p3 and pixels q0, q1, q2 and q3 ofneighboring blocks P and Q for determining filtering strength;

FIG. 3 shows a process of determining filtering strength in theH.264/AVC standard;

FIG. 4 is a block diagram showing a configuration of an encodingapparatus to which a deblocking filtering apparatus according to one ormore embodiments of the present disclosure is applied;

FIG. 5 is a block diagram showing a configuration of a deblocking filterunit according to one or more embodiments of the present disclosure;

FIG. 6 is a flow diagram showing a process of determining filteringstrength according to one or more embodiments of the present disclosure;

FIG. 7 is a flow diagram showing a process of determining filteringstrength according to another embodiment of the present disclosure;

FIGS. 8A and 8B are exemplary diagrams for describing a process ofdetermining filtering strength according to whether a block boundarydirection and an intra prediction direction are identical to each other;

FIG. 9 is a flow diagram showing a process of determining filteringstrength according to still another embodiment of the presentdisclosure;

FIGS. 10A and 10B are flow diagrams showing a process of determiningfiltering strength according to yet another embodiment of the presentdisclosure;

FIGS. 11, 12A, 12B, 12C, 12D and 13 are diagrams for describing aprocess of determining a target pixel to be filtered by a filteringpixel determination unit according to one or more embodiments of thepresent disclosure;

FIG. 14 is a block diagram showing a configuration of a decodingapparatus to which a deblocking filtering apparatus according to one ormore embodiments of the present disclosure is applied; and

FIGS. 15A and 15B are diagrams showing an intra prediction mode definedin the H.264/AVC standard.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings. In the followingdescription, like reference numerals designate like elements althoughthey are shown in different drawings. Further, in the followingdescription of the present embodiments, a detailed description of knownfunctions and configurations incorporated herein will be omitted for thepurpose of clarity.

Additionally, in describing the components of the present disclosure,there may be terms used like first, second, A, B, (a), and (b). Theseare solely for the purpose of differentiating one component from theother but not to imply or suggest the substances, order or sequence ofthe components. If a component were described as ‘connected’, ‘coupled’,or ‘linked’ to another component, they may mean the components are notonly directly ‘connected’, ‘coupled’, or ‘linked’ but also areindirectly ‘connected’, ‘coupled’, or ‘linked’ via a third component.

FIG. 4 is a block diagram showing a configuration of an encodingapparatus to which a deblocking filtering apparatus according to one ormore embodiments of the present disclosure is applied.

Referring to FIG. 4, a moving picture encoding apparatus, to which adeblocking filtering apparatus according to one or more embodiments ofthe present disclosure is applied, may include a prediction unit 410, aresidual data encoding unit 420, a residual data decoding unit 430, anentropy encoding unit 440, an encoded data generation unit 450, and adeblocking filter unit 460.

A video input to be encoded may be input in units of blocks, forexample, macroblocks. For convenience of description, in the embodimentof the present disclosure, the macroblock is defined as a 16×16 form inthe same manner as the H.264/AVC standard. However, the macroblock formmay be M×N. In this case, M and N may be greater than 16, or may be thesame or different integers. In addition, there is no necessity to limitthe block unit to specific unit called a macroblock in the related art.That is, it should be understood that the block unit is a conceptencompassing units such as coding unit (CU) or largest CU (LCU).

The prediction unit 410 receives any one of macroblock modes forpredicting a current block and generates a prediction block bypredicting a current block to be encoded in unit corresponding to thereceived macroblock mode (for example, 16×16, 16×8, 8×16, 8×8, 8×4, 4×8,or 4×4 pixel unit).

That is, the prediction unit 410 predicts the current block by usingintra prediction or inter prediction, and generates the prediction blockhaving a predicted pixel value as a pixel value of each pixel.

In the case of the intra prediction, the prediction unit 410 generatesan intra prediction block of the current block by using available pixelvalues of pixels located spatially neighboring the current block. Inthis case, error values between the current block and the intraprediction block with respect to the available intra prediction modesare calculated, and the intra prediction block is generated by applyingthe intra prediction mode having the minimum error value. In addition,the intra prediction mode having the minimum error value is encoded, andinformation about the intra prediction mode is provided to the encodeddata generation unit 450.

In the embodiment of the present disclosure, as shown in FIGS. 15A and15B, nine intra prediction modes (in the case of 4×4 and 8×8 intrablocks) and four intra prediction modes (in the case of 16×16 intrablock) having directions in the same manner as the H.264/AVC standardare taken as an example, but the intra prediction modes may be definedin more various methods. For example, L intra prediction modes havingdirections in an M×N intra prediction block may be used. In particular,M and N may be greater than 16 and may be the same or differentintegers.

In the case of the inter prediction, the prediction unit 410 calculateserror values between the current block and the inter prediction blockwith respect to all available reference pictures located temporallyneighboring the current picture, and generates the inter predictionblock of the reference picture having the minimum error value as theinter prediction block of the current block. In this case, a motionvector is estimated based on the positions of the current block and theinter prediction block having the minimum error value. In addition, theestimated motion vector and index information of the reference pictureare provided to the encoded data generation unit 450.

A residual block is generated by subtracting the prediction blockgenerated by using the intra or inter prediction from the current block.That is, the residual block is generated by calculating a differencebetween an original pixel value of each pixel of the current block and apredicted pixel value of each pixel of the prediction block. Thegenerated residual block is provided to the residual data encoding unit420.

The residual data encoding unit 420 transforms and quantizes theresidual block, and generates an encoded residual block. In this case,the transform scheme may use various methods for transforming aspace-domain signal into a frequency-domain signal, such as Hadamardtransform, discrete cosine transform, and the like. The quantizationscheme may use various quantization methods, such as uniformquantization with dead zone, quantization matrix, and the like.

According to one or more embodiments of the present disclosure, the sizeof the transform block may not exceed the size of the prediction block.For example, when the size of the prediction block is 16×16, the 16×16,16×8, 8×16, 8×8, 8×4, 4×8, or 4×4 transform block, which does not exceed16×16, may be used. When the size of the prediction block is 8×8, the8×8, 8×4, 4×8, or 4×4 transform block, which does not exceed 8×8, may beused. When the size of the prediction block is 4×4, only the 4×4transform block may be used. In addition, the size of the transformblock may be selected based on rate-distortion optimization. When thesize of the transform block does not exceed the size of the predictionblock, the residual data encoding unit 420 divides the residual blockinto subblocks having the same size as that of the transform block, andsequentially transforms and quantizes the subblocks.

According to another embodiment of the present disclosure, the size ofthe transform block may exceed the size of the prediction block. Forexample, when the size of the prediction block is 16×16, the 32×16,16×32, 32×32, 64×32, 32×64, or 64×64 transform block may be used. Whenthe size of the transform block is larger than the size of theprediction block, the residual data encoding unit 420 generates acombined residual block having the same size as that of the transformblock by combining a plurality of residual blocks spatially neighboringone another, and transforms and quantizes the combined residual block.

The residual data decoding unit 430 reconstructs the residual block byinversely quantizing and inversely transforming the residual blocktransformed and quantized by the residual data encoding unit 420. Theinverse quantization and the inverse transform are achieved by inverselyperforming the transform process and the quantization process that wereperformed by the residual data encoding unit 420. The inversequantization and the inverse transform may be implemented in variousmethods. For example, the transform and inverse transform or thequantization and inverse quantization having the same process, which arein a prearrangement between the residual data encoding unit 420 and theresidual data decoding unit 430, may be used. Alternatively, theresidual data decoding unit 430 may perform the inverse quantization andinverse transform by inversely performing the transform and quantizationprocess of the residual data encoding unit 420 by using informationabout the transform and quantization process (for example, transformsize, transform shape, quantization type, and the like) generated andtransferred by the transform and quantization process of the residualdata encoding unit 420.

The residual block output from the residual data decoding unit 430 isadded to the prediction block reconstructed by the prediction unit 410and then generated as the reconstructed block.

The entropy encoding unit 440 performs entropy encoding on the residualblock output from the residual data encoding unit 420. Although notshown in the embodiment of the present disclosure, if necessary, theentropy encoding unit 440 may encode various pieces of informationnecessary for decoding encoded bitstream, as well as the residual block.The various pieces of information necessary for decoding the encodedbitstream may include information about the block type, informationabout the intra prediction mode when the prediction mode is the intraprediction mode, information about the motion vector when the predictionmode is the inter prediction mode, and information about the transformand quantization type.

The entropy encoding unit 440 may use various entropy encoding methods,for example, context adaptive variable length coding (CAVLC) and contextadaptive binary arithmetic coding (CABAC).

The encoded data generation unit 450 arranges the entropy-encodedresidual block, the macroblock mode, and the encoded predictioninformation (for example, information about the intra prediction mode inthe case of the intra encoding, and information about the referencepicture index and the motion vector in the case of the inter encoding)and outputs the encoded data.

The deblocking filter unit 460 filters the reconstructed current blockso as to reduce blocking artifact generated by the block-unit predictionand quantization. According to one or more embodiments of the presentdisclosure, the deblocking filter unit 460 may perform adaptivedeblocking filtering by using information about the block-unitprediction to be transmitted together with the reconstructed currentblock (for example, information about the intra prediction mode and theintra prediction block size in the case of the intra encoding, andinformation about the reference picture index and the motion vector inthe case of the inter encoding) or information about the transform andquantization (for example, information about the size and shape of thetransform block and the quantization parameter). In this case, theinformation about the prediction or quantization may be transferred tothe deblocking filter unit 460 of the encoding apparatus, or may begenerated as the encoded data by the encoded data generation unit 450and transferred to the decoding apparatus.

The deblocking filter unit 460 performs deblocking filtering on thepixels around the block boundary. In the embodiment of the presentdisclosure, on an assumption of using the transform block of 4×4 unit,the block unit and filtering order, to which the deblocking filtering isapplied, are exemplified as shown in FIG. 1. However, the transformblock may be defined in various methods. In addition, the deblockingfiltering in accordance with the conventional H.264 standard filters theboundary pixels of the 4×4 transform block or the 8×8 transform block.However, according to the present disclosure, as will be described inthe following embodiments, pixels of the boundary region betweenprediction blocks as well as pixels of the boundary region betweentransform blocks may be adaptively deblocking-filtered according toprediction information of the prediction blocks.

Hereinafter, the deblocking filter unit 460 will be described in moredetail with reference to FIGS. 5 to 13.

FIG. 5 is a block diagram showing the configuration of the deblockingfilter unit according to one or more embodiments of the presentdisclosure.

Referring to FIG. 5, the deblocking filter unit 460 may include afiltering strength determination unit 510, a filtering pixeldetermination unit 520, and a filter unit 530.

The filtering strength determination unit 510 performs a filteringstrength determining process so as to adaptively remove blockingartifact generated by the block-unit prediction and quantization anddetermine whether the boundary to be filtered corresponds to theboundary the image actually has or corresponds to the boundary generatedby the block-unit prediction and quantization. Whether to filter therelevant boundary and the filtering execution strength may bedifferently applied according to the filtering strength obtained throughthe filtering strength determination unit 510.

The filtering strength may be adjusted in various methods.

As the simplest method, the filtering strength may be adjusted bycontrolling a filter cutoff frequency. For example, the filteringstrength may be increased by setting the filter such that the cutofffrequency is further lowered, and the filtering strength may bedecreased by setting the filter such that the cutoff frequency isfurther raised. In this manner, the filtering strength may be adjusted.

As another method, the filtering strength may be increased or decreasedby controlling the filter characteristic such that smoothing isperformed much more or much less.

As still another method, the filtering strength is adjusted such that amaximum changeable range of a pixel value changed by filtering islimited. That is, the filtering strength is adjusted such that adifference between a pixel value after filtering and a pixel valuebefore filtering exceeds a predetermined threshold value (tc). Morespecifically, the value after filtering may be limited to a range of+/−tc from the value before filtering (hereinafter, referred to as A),that is, a range of A−tc to A+tc. This process is generally referred toas clipping. For example, comparing the case of tc=3 and the case oftc=4, it may be considered that the case of tc=3 is weaker in filteringstrength than tc=4. This is because a variation of a value changeable byfiltering is limited as much. That is, the filtering strength may beadjusted by regulating the clipping threshold tc.

As yet another method, the filtering strength may be adjusted bydifferently setting the BS. This method corresponds to one method or acombination of one or more methods of setting one parameter adjustingthe filtering strength as the BS and then adjusting the above-describedfiltering strength with respect to each BS value. For example, when theBS is strong, the above methods may be appropriately combined to makethe filtering relatively strong. On the other hand, when the BS is weak,the above methods may be appropriately combined to make the filteringrelatively weak.

In the case where the current block and at least one of blocksneighboring the current block have been intra-predicted, the filteringstrength determination unit 510 may adaptively determine the filteringstrength, based on at least one piece of information amongexistence/nonexistence of a nonzero transform coefficient in the currentblock and at least one of the neighboring blocks, intra predictioninformation of the current block and the neighboring blocks, macroblockmode information of the current block and the neighboring blocks, andblock boundary direction.

For example, in the case where the current block and at least one of theblocks neighboring the current block have been intra-predicted, when thenonzero transform coefficient exists in the current block and at leastone of the neighboring blocks, the filtering strength determination unit510 may assign higher filtering strength than the case where the nonzerotransform coefficient does not exist.

In addition, in the case where the current block and at least one of theblocks neighboring the current block have been intra-predicted, thefiltering strength determination unit 510 may adaptively determine thefiltering strength according to whether intra prediction information ofthe current block and intra prediction information of the neighboringblock are identical to each other. For example, in the case where theintra prediction information of the current block and the intraprediction information of the neighboring block are not identical toeach other, the filtering strength determination unit 510 may assignhigher filtering strength than the case where the intra predictioninformation of the current block and the intra prediction information ofthe neighboring block are identical to each other. Furthermore, in thecase where the current block and the neighboring block have identicalintra prediction information, the filtering strength determination unit510 may perform no deblocking filtering. The intra predictioninformation may include at least one of the intra prediction mode andthe intra prediction block size.

In addition, in the case where the current block and at least one of theblocks neighboring the current block have been intra-predicted, thefiltering strength determination unit 510 may adaptively determine thefiltering strength, based on whether the macroblock mode information ofthe current block and the macroblock mode information of the neighboringblock are identical to each other. For example, in the case where thecurrent block and the neighboring block do not have identical macroblockmode information, the filtering strength determination unit 510 mayassign higher filtering strength than the case where the current blockand the neighboring block have identical macroblock mode information.

In addition, in the case where the current block and at least one of theblocks neighboring the current block have been intra-predicted, thefiltering strength determination unit 510 may adaptively determine thefiltering strength according to whether the block boundary direction andthe intra prediction mode (prediction direction) are identical to eachother. For example, in the case where the block boundary direction andthe intra prediction direction are not identical to each other, thefiltering strength determination unit 510 may assign higher filteringstrength than the case where the block boundary direction and the intraprediction direction are identical to each other.

On the other hand, in the case where neither of the current block andthe neighboring block has been intra-predicted, the filtering strengthdetermination unit 510 may determine the filtering strength, based onexistence/nonexistence of the nonzero transform coefficient in thecurrent block and at least one of the neighboring blocks and the interprediction information. For example, in the case where the nonzerotransform coefficient exists in the current block and at least one ofthe neighboring blocks, the filtering strength determination unit 510may assign higher filtering strength than the case where the nonzerotransform coefficient does not exist in the current block and at leastone of the neighboring blocks. In addition, inter prediction informationof the current block is compared with inter prediction information ofthe neighboring block. If the inter prediction information of thecurrent block and the inter prediction information of the neighboringblock are not identical to each other, the filtering strengthdetermination unit 510 may assign higher filtering strength than thecase where the inter prediction information of the current block and theinter prediction information of the neighboring block are identical toeach other. Furthermore, if the inter prediction information of thecurrent block and the inter prediction information of the neighboringblock are identical to each other, the filtering strength determinationunit 510 may perform no deblocking filtering. The inter predictioninformation may include information about reference picture/referenceframe, motion vector, and the like.

On the other hand, if the current block is the intra prediction block,the filtering strength determination unit 510 may determine thefiltering strength in consideration of only encoding information of thecurrent block, instead of encoding information of the current block andall neighboring blocks. That is, if the current block is the intraprediction block, the filtering strength determination unit 510 maydetermine the filtering strength according to at least one of whetherthe nonzero transform coefficient exists in the current block andwhether the deblocking direction and the intra prediction direction areidentical to each other.

For example, if the nonzero transform coefficient exists in the currentblock, the filtering strength determination unit 510 may assign higherfiltering strength than the case where the nonzero transform coefficientdoes not exist in the current block. In addition, if the block boundarydirection and the intra prediction direction are not identical, thefiltering strength determination unit 510 may assign higher filteringstrength than the case where the block boundary direction and the intraprediction direction are identical. Details will be described below withreference to FIGS. 9, 10A and 10B. The deblocking direction refers to adirection in which the deblocking filtering is performed. That is, asshown in FIGS. 10A and 10B, the deblocking direction is a directionforming a right angle with the block boundary to be deblocked.Alternatively, as shown in FIGS. 12A, 12B, 12C and 12D, the deblockingdirection may be a direction forming a predetermined angle with theblock boundary. In addition, when determining whether the deblockingdirection of the current block and the intra prediction direction areidentical to each other, if the deblocking direction and the intraprediction direction are not exactly identical to each other but withina predetermined range of difference, the deblocking direction and theintra prediction direction may be considered to be the same depending onimplementations.

Hereinafter, the process of determining the filtering strength by thefiltering strength determination unit 510 will be described in moredetail with reference to various embodiments.

FIG. 6 is a flow diagram showing a process of determining the filteringstrength according to one or more embodiments of the present disclosure.

Referring to FIG. 6, it is determined whether at least one of a block Pand a block Q neighboring a boundary to be filtered, as shown in FIG. 2,has been predicted in an intra mode (S610). If the block P or the blockQ is the intra mode, steps S620 and S630 are sequentially performed; ifnot, steps S640 and 650 are sequentially performed.

When it is determined in step S610 that the block P or the block Q isthe intra prediction block, it is determined whether a nonzero transformcoefficient exists in residual data of the block P and the block Q(S620). When the nonzero transform coefficient does not exist in theresidual data of the block P and the block Q, step S630 is performed;otherwise, a filtering strength value becomes 4. That is, in the casewhere the nonzero transform coefficient exists in the residual data ofthe block P and the block Q, blocking artifact is significantlygenerated by transform and quantization. Therefore, strong filtering isperformed. For example, the filtering strength is adaptively determinedaccording to whether the block boundary is the macroblock boundary orwhich block uses intra encoding. Strong filtering is applied to a regionwhere block distortion easily occurs. In the opposite case, filtering isminimized. In this manner, video quality degradation can be preventedfrom occurring by unnecessary filtering. If blocking artifact severelyoccurs, even the inside of the block may be affected. Therefore,blocking artifact is reduced by performing filtering on much more pixelswithin the block. For example, referring to Equations 1 and 2, which areto be described below, blocking artifact may be alleviated by performingfiltering on only p1, p0, q0, and q1 in the case where blocking artifactis not severe, as expressed in Equation 1, and by performing filteringon p2, p1, p0, q0, q1, and q2 in the case where blocking artifact issevere, as expressed in Equation 2.

When step S620 determines that the nonzero transform coefficient doesnot exist in the residual data of the block P and the block Q, it isdetermined whether the intra prediction information of the block P andthe intra prediction information of the block Q are identical to eachother (S630). In the embodiment of the present disclosure, when theintra prediction block sizes and the intra prediction modes of the blockP and the block Q are identical, the intra prediction information of theblock P and the intra prediction information of the block Q aredetermined as identical to each other. For example, when the block P isthe intra prediction mode and the block Q is the inter prediction mode,when the block P is the intra 16×16 prediction mode and the block Q isthe intra 4×4 prediction mode, or when the block P is the intra 4×4zeroth prediction mode and the block Q is the intra 4×4 first predictionmode, the intra prediction information of the block P and the intraprediction information of the block Q are determined as not identical toeach other. In the embodiment of the present disclosure, the determiningprocess of step S620 has been defined on the assumption that the intraprediction method of the H.264/AVC standard is used, but the determiningprocess of step S620 may also be defined in various methods according toapplications and purposes.

When step S620 determines that the intra prediction information of theblock P and the intra prediction information of the block Q areidentical to each other, the filtering strength value becomes 0;otherwise, the filtering strength value becomes 3. That is, since theblock P and the block Q use different prediction methods when the intraprediction information of the block P and the intra predictioninformation of the block Q are not identical to each other, there occursblocking artifact caused by prediction. Therefore, weaker deblockingfiltering is performed as compared with the case where the nonzerotransform coefficient exists in the residual data of the block P or theblock Q. Since the block P and the block Q use the same predictionmethod when the intra prediction mode of the block P and the intraprediction mode of the block Q are identical to each other, there is nooccurrence of blocking artifact caused by prediction. Therefore,deblocking filtering is not performed.

When step S610 determines that neither of the block P and the block Q isthe intra prediction block, it is determined whether the nonzerotransform coefficient exists in the residual data of the block P or theblock Q (S640). When the nonzero transform coefficient does not exist inthe residual data of the block P or the block Q, step S650 is performed;otherwise, a filtering strength value becomes 2.

When step S640 determines that the nonzero transform coefficient doesnot exist in the residual data of the block P or the block Q, it isdetermined whether the inter prediction information of the block P andthe inter prediction information of the block Q are identical to eachother (S650). When the block P and the block Q use different referencepictures or make reference to different blocks while using the samereference picture, or when the block P and the block Q have differentmotion vector values, the inter prediction information of the block Pand the inter prediction information of the block Q are determined asnot identical to each other.

When it is determined in step S650 that the inter prediction informationof the block P and the inter prediction information of the block Q areidentical to each other, the filtering strength value becomes 0;otherwise, the filtering strength value becomes 1.

FIG. 7 is a flow diagram showing a process of determining filteringstrength according to another embodiment of the present disclosure.

Since steps S710, S760 and S770 of FIG. 7 are substantially identical tosteps S610, S640 and S650 of FIG. 6, steps S720 to S750 will bedescribed in more detail.

When step S710 determines that at least one of the block P and the blockQ has been intra-predicted, it is determined whether the macroblock modeinformation of the block P and the macroblock mode information of theblock Q are identical to each other (S720). When the macroblock modeinformation of the block P and the macroblock mode information of theblock Q are not identical to each other, the filtering strength valuebecomes 4.

On the other hand, when the macroblock mode information of the block Pand the macroblock mode information of the block Q are identical to eachother, it is determined whether the nonzero transform coefficient existsin at least one of the block P and the block Q (S730). When the nonzerotransform coefficient exists in at least one of the block P and theblock Q, the filtering strength value becomes 3.

When it is determined in step S730 that no transform coefficient existsin the block P and the block Q, the process proceeds to step S740 todetermine whether the intra prediction information of the block P andthe intra prediction information of the block Q are identical to eachother. When it is determined that the intra prediction mode of the blockP and the intra prediction mode of the block Q are not identical to eachother, the filtering strength value becomes 2.

On the other hand, when the intra prediction mode of the block P isdetermined to be identical to the intra prediction mode of the block Q,it is determined whether the block boundary direction and the intraprediction direction are identical to each other (S750). When two blocksare neighboring each other in a horizontal direction, the block boundary(that is, edge) is vertically formed. On the other hand, when two blocksare neighboring each other in a vertical direction, the block boundary(that is, edge) is horizontally formed. Therefore, in step S750, theintra prediction direction and the block boundary direction (that is,whether the block edge is vertical or horizontal) are compared with eachother. In the case where the intra prediction direction and the blockboundary direction are not identical to each other, higher filteringstrength is assigned than the case where the intra prediction directionand the block boundary direction are identical to each other. That is,as shown in FIG. 8A, when the block boundary (that is, edge) directionand the intra prediction direction are identical to each other, thefiltering strength of 0 is assigned. As shown in FIG. 8B, when the blockboundary (that is, edge) direction and the intra prediction directionare different from each other, the filtering strength of 1 is assigned.

In the embodiment of the present disclosure, which has been describedabove with reference to FIGS. 7 and 8, the filtering strength fordeblocking filtering is assigned with reference to encoding informationof the current block and all neighboring blocks. However, the presentdisclosure is not limited thereto. As will be described below, thefiltering strength for deblocking filtering may also be assigned withreference to only encoding information of the current block. Forexample, the filtering strength can be adaptively assigned based on atleast one of whether the nonzero transform coefficient exists in thecurrent block and whether the intra prediction direction of the currentblock and the deblocking direction are identical to each other.

FIG. 9 is a flow diagram showing a process of determining filteringstrength according to still another embodiment of the presentdisclosure.

Since steps S940, S950 and S960 of FIG. 9 are substantially identical tosteps S610, S640 and S650 of FIG. 6, steps S910, S920 and S930 will bedescribed below in more detail.

First, it is determined whether the block P being the current block P isthe intra-predicted block (S910). When it is determined that the block Pis not the intra-predicted block, the process proceeds to steps S940 toS960 which are substantially identical to steps S610, S640 and S650.

On the other hand, when it is determined in step S910 that the block Pbeing the current block is the intra-predicted block, the filteringstrength for deblocking filtering is determined with reference to onlyencoding information of the current block, without consideringinformation of the blocks neighboring the current block, for example,according to whether the nonzero transform coefficient exists in thecurrent block, whether the deblocking direction of the current block andthe intra prediction direction (prediction mode) are identical to eachother, and the like.

For example, when the block P being the current block is theintra-predicted block, it is determined whether the nonzero transformcoefficient exists in the block P (S920). In the case where the nonzerotransform coefficient exists, higher filtering strength may be assignedthan the case where the nonzero transform coefficient does not exist.For example, the filtering strength of 2 may be assigned.

On the other hand, in the case where the nonzero transform coefficientdoes not exist in the block P being the current block, it is determinedwhether the deblocking direction of the block P and the intra predictiondirection of the block P determined according to the intra predictionmode are identical to each other (S930). In the case where thedeblocking direction of the block P and the intra prediction directionof the block P are not identical to each other, lower filtering strengthis assigned than the case where the nonzero transform coefficientexists. For example, the filtering strength of 0 is assigned. In thecase where the deblocking direction of the block P and the intraprediction direction of the block P are identical to each other, lowerfiltering strength is assigned than the case where the deblockingdirection of the block P and the intra prediction direction of the blockP are not identical to each other. For example, the filtering strengthof 0 is assigned.

As shown in FIG. 10A, in the case where the deblocking direction of theblock P being the current block and the intra prediction direction ofthe block P are not identical to each other, the filtering strengthbecomes 1.

On the other hand, as shown in FIG. 10B, in the case where thedeblocking direction of the block P and the intra prediction directionof the block P are identical to each other, lower filtering strength isassigned than the case where they are not identical to each other. Forexample, the filtering strength of 0 is assigned.

As described above in still another embodiment of the presentdisclosure, in the case where the current block is the intra predictionblock, the filtering strength for deblocking filtering may be determinedwith reference to only the encoding information of the current block,without considering both of the encoding information of the currentblock and the encoding information of the neighboring block.

For example, referring to FIG. 10A, in the case where the block P beingthe current block has been intra-predicted, if the nonzero transformcoefficient does not exist in the block P and the deblocking directionand the intra prediction direction are identical to each other, it meansthat blocking artifact caused by prediction and quantization does notoccur in the boundary of the block P. That is, since the predicted valueof the block P is predicted from an arbitrary neighboring block,blocking artifact caused by prediction does not occur. Since the nonzerotransform coefficient does not exist in the block P, there is also nooccurrence of blocking artifact caused by quantization. Therefore, thefiltering strength for deblocking may be determined with reference toonly the encoding information of the current block, such as whether thecurrent block is the intra prediction block, whether the nonzerotransform coefficient exists in the current block, or whether thedeblocking direction of the current block and the intra predictiondirection are identical to each other.

In FIG. 9, although the filtering strengths determined in steps S920 andS930 are described as identical to the filtering strengths determined insteps S940, S950 and S960, the filtering strengths of both cases may notbe identical. All or part of them may have different values.

The detailed embodiments of determining the filtering strength have beendescribed with reference to FIGS. 6 to 10, in the case where at leastone of the current block and the neighboring block is intra-predicted orin the case where the current block is intra-predicted. However, it isapparent that these embodiments are merely exemplary for implementingthe present disclosure and not to limit the scope of the presentdisclosure. For example, in order to determine the filtering strength,just one or two or more of the information about existence/nonexistenceof the nonzero transform coefficient, the intra prediction informationof the current block and the neighboring block, the macroblock modeinformation of the current block and the neighboring block, the blockboundary direction, and the deblocking direction may be used. Inaddition, in the case where two or more pieces of information are used,the filtering strengths may be determined by sequences other than thesequences of FIGS. 6, 7 and 9.

Referring again to FIG. 5, the deblocking filter unit 460 may furtherinclude a filtering pixel determination unit 520 that determines atarget pixel to be deblocking-filtered with respect to blocks havingnonzero filtering strength.

In particular, in the case where at least one of the current block andthe neighboring block is intra-predicted, the filtering pixeldetermination unit 520 may determine the target pixel, based on theintra prediction information. For example, the filtering pixeldetermination unit 520 may determine the number of target pixels, basedon the intra prediction block size. Furthermore, the position of thetarget pixel, that is, the filtering direction, may also be determinedbased on the intra prediction mode. In other words, the position of thetarget pixel, that is, the filtering direction, may be set as the sameconcept as the above-described deblocking direction, but the filteringpixel determination unit 520 may also newly determine the filteringdirection (position of the target pixel), based on the intra predictionmode. In order to avoid confusion with the term “deblocking direction”,the deblocking direction newly determined by the filtering pixeldetermination unit 520 is newly defined as the filtering direction(position of the target pixel).

Embodiments of determining the target pixel by the filtering pixeldetermination unit 520 will be described below with reference to FIGS.11 to 13.

Referring to FIG. 11, the filtering pixel determination unit 520 maydetermine the number of pixels to be deblocking-filtered at the boundaryof intra prediction blocks using different intra prediction sizes. Thatis, the filtering pixel determination unit 520 can identify the size ofthe intra prediction block and determine the number of pixels to bedeblocking-filtered. For example, in the case where the boundary betweenan intra 4×4 prediction block and another intra 4×4 prediction block isdeblocking-filtered, the number of the pixels to be deblocking-filteredin the block P is four (p0, p1, p2, p3), and the number of the pixels tobe deblocking-filtered in the block Q is four (q0, q1, q2, q3). However,in the case where the boundary between the intra 16×16 prediction blockand the intra 4×4 prediction block is deblocking-filtered, the number ofthe pixels to be deblocking-filtered in the block P using the intra 4×4prediction may be four (p0, p1, p2, p3), and the number of the pixels tobe deblocking-filtered in the block Q using the intra 16×16 predictionmay be six (q0, q1, q2, q3, q4, q5). This means that as the size of theintra prediction block is larger, more pixels may be subject todeblocking-filtering.

Referring to FIGS. 12A, 12B, 12C and 12D, the filtering pixeldetermination unit 520 may determine the positions of pixels to bedeblocking-filtered at the boundary of intra prediction blocks usingdifferent intra prediction mode. That is, the filtering pixeldetermination unit 520 can identify the intra prediction block mode anddetermine the positions of the pixels to be deblocking-filtered.

For example, in the case where the boundary between a 4×4 predictionblock (mode 1) and another intra 4×4 prediction block (mode 1) isdeblocking-filtered, the positions of the pixels to bedeblocking-filtered with respect to the block P are a horizontaldirection (p0, p1, p2, p3), and the positions of the pixels to bedeblocking-filtered with respect to the block Q are a horizontaldirection (q0, q1, q2, q3) (FIG. 12A). However, in the case where theboundary between an intra 4×4 prediction block (mode 3) and anotherintra 4×4 prediction block (mode 3) is deblocking-filtered, thepositions of the pixels to be deblocking-filtered in the block P are adiagonal down-left direction (p0, p1, p2, p3), and the positions of thepixels to be deblocked-filtered in the block Q are a diagonal down-leftdirection (q0, q1, q2, q3) (FIG. 12B). In the case where the boundarybetween an intra 4×4 prediction block (mode 4) and another intra 4×4prediction block (mode 4) is deblocking-filtered, the positions of thepixels to be deblocking-filtered in the block P are a diagonaldown-right direction (p0, p1, p2, p3), and the positions of the pixelsto be deblocked-filtered in the block Q are a diagonal down-rightdirection (q0, q1, q2, q3) (FIG. 12C). This means that the positions ofthe pixels to be deblocking-filtered may be determined considering thedirection according to the intra prediction mode.

In addition, the same idea can be applied even when the prediction modesof the neighboring intra prediction blocks are different. For example,in the case where the boundary between an intra 4×4 prediction block(mode 4) and another intra 4×4 prediction block (mode 1) isdeblocking-filtered, the positions of the pixels to bedeblocking-filtered in the block Q are a diagonal down-right directionhorizontal direction (q0, q1, q2, q3), and the positions of the pixelsto be deblocking-filtered in the block P are a horizontal direction (p0,p1, p2, p3) (FIG. 12D).

On the other hand, the filtering pixel determination unit 520 maydetermine the number and positions of the pixels to bedeblocking-filtered at the boundary of intra prediction blocks usingdifferent intra prediction block sizes and different prediction modes.That is, the filtering pixel determination unit 520 can identify theintra prediction block size and the prediction mode, and determine thenumber and positions of the pixels to be deblocking-filtered.

For example, referring to FIG. 13, in the case where the boundarybetween the intra 16×16 prediction block (horizontal mode) and the intra4×4 prediction block (mode 4) is deblocking-filtered, the number andpositions of the pixels to be deblocking-filtered in the block P arefour (p0, p1, p2, p3) and a diagonal down-right direction, and thenumber and positions of the pixels to be deblocking-filtered in theblock Q are six (q0, q1, q2, q3, q4, q5) and a horizontal direction.

Referring again to FIG. 5, when the filtering strength of thecorresponding block and the pixels to be filtered are determined by thefiltering strength determination unit 510 and the filtering pixeldetermination unit 520, the deblocking filtering is performed by thefilter unit 530.

The filter unit 530 performs filtering with reference to the number andpositions of the pixels to be filtered, which are determined by thefiltering pixel determination unit 520 according to the filteringstrength of the corresponding block determined by the filtering strengthdetermination unit 510.

Hereinafter, the filtering method according to the embodiment of thepresent disclosure will be described in detail.

In the case whether the filtering strength is lower than four and thenumber of the pixels to be filtered is equal to or less than four, thefiltering is performed as expressed in Equation 1 below.

$\begin{matrix}{{\Delta = {{Clip}\lbrack {{- {tc}},{tc},\frac{ { \{ {( {{q\; 0} - {p\; 0}} ){\operatorname{<<}2+(p1-q1}}  ) + 4} \}}{8}} \rbrack}}{{p^{\prime}0} = {{p\; 0} + \Delta}}{{q^{\prime}0} = {{q\; 0} + \Delta}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

In Equation 1, a value of tc is determined by a value of β which isdetermined by the absolute differences |p2−p0| and |q2−q0| of the pixelvalues of the pixels to be deblocking-filtered and quantizationcoefficient. In Equation 1, Clip takes a value of{(q0−p0)<<2+(p1−q1)+4}/8, and clipping is performed such that the valueof Clip does not exceed −tc and +tc.

As expressed in Equation 1, pixel values p′0 and q′0 which are thedeblocking-filtered pixel values of p0 and q0 may be determined througha 4-tap finite impulse response (FIR) filter using q1, q0, p0 and p1. Inaddition, the filtering may be performed on the pixel values of p′1 andq′1 through a similar method. The number of the pixels to be filtered inthe block P is four, and the number of the pixels to be filtered in theblock Q is four. The number of the pixels filtered in the block P istwo, and the number of the pixels filtered in the block Q is two.

In the case where the filtering strength is four and the number of thepixels to be filtered is equal to or less than four, the filtering isperformed as expressed in Equation 2.

$\begin{matrix}{{q^{\prime}0} = \frac{{1 \times q\; 2} + {2 \times q\; 1} + {2 \times q\; 0} + {2 \times p\; 0} + {1 \times p\; 1} + 4}{8}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Equation 2 is an example of equation for obtaining q′0 in the case wherethe filtering strength is four. As expressed in Equation 2, 5-tapfiltering using q2, q1, q0, p0 and p1 is applied. In addition, filteringis performed on the pixel values p′2, p′1, p′0, q′0, q′1 and q′2 byusing a similar manner. The number of the pixels to be filtered in theblock P is four, and the number of the pixels to be filtered in theblock Q is four. The number of the pixels filtered in the block P isthree, and the number of the pixels filtered in the block Q is three.

In the embodiment of the present disclosure, deblocking filtering ofdifferent numbers and positions is provided according to the intraprediction block size and the intra prediction mode. That is, as shownin FIGS. 7 and 9, the deblocking filtering may be made to influence moreinner pixels.

Therefore, the embodiment of the present disclosure exemplifies afiltering method in the case where the number of pixels to be filteredis six as expressed in Equation 3 below.

$\begin{matrix}{{q^{\prime}0} = \frac{\begin{matrix}{{1 \times q\; 3} + {2 \times q\; 2} + {3 \times q\; 1} +} \\{{4 \times q\; 0} + {3 \times p\; 0} + {2 \times p\; 1} + {1 \times p\; 2} + 8}\end{matrix}}{16}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

Equation 3 is an example of equation for obtaining q′0 in the case wherethe filtering strength is four. As expressed in Equation 3, 7-tapfiltering using q3, q2, q1, q0, p0, p1 and p2 is applied. In addition,filtering is performed on the pixel values p′3, p′2, p′1, p′0, q′0, q′1,q′2 and q′3 in a similar manner. The number of the pixels to be filteredin the block P is six, and the number of the pixels to be filtered inthe block Q is six. The number of the pixels filtered in the block P isfour, and the number of the pixels filtered in the block Q is four.

As in the example of FIG. 13, in the case where the number of the pixelsto be filtered is different in between the block P and the block Q,Equation 2 may be applied to the block P and Equation 3 may be appliedto the block Q. Here, the number of the pixels to be filtered in theblock P is four, and the number of the pixels to be filtered in theblock Q is six. The number of the pixels to be filtered in the block Pis two, and the number of the pixels to be filtered in the block Q isfour.

FIG. 14 is a block diagram showing a configuration of a decodingapparatus to which a deblocking filtering apparatus according to one ormore embodiments of the present disclosure is applied.

The decoding apparatus, to which the deblocking filtering apparatusaccording to one or more embodiments of the present disclosure isapplied, may include an encoded data extraction unit 1410, an entropydecoding unit 1420, a residual data decoding unit 1430, a predictionunit 1440, and a deblocking filter unit 1450.

The encoded data extraction unit 1410 extracts and analyzes receivedencoded data and transfers data about a residual block to the entropydecoding unit 1420, and transfers the macroblock mode and the encodedprediction information (for example, the intra prediction mode in thecase of the intra encoding, and the information about the referencepicture index and the motion vector in the case of the inter encoding)to the prediction unit 1440.

The entropy decoding unit 1420 generates a quantized residual block byperforming entropy decoding on the residual block received from theencoded data extraction unit 1410. Although not shown in the embodimentof the present disclosure, if necessary, the entropy decoding unit 1420may decode various pieces of information necessary for decoding encodeddata, as well as the residual block. The various pieces of informationnecessary for decoding the encoded data may include information aboutthe block type, information about the intra prediction mode when theprediction mode is the intra prediction mode, information about themotion vector when the prediction mode is the inter prediction mode, andinformation about the transform and quantization type. The entropydecoding unit 1420 may be defined in various methods according to theentropy encoding method used in the entropy encoding unit 440 of theencoding apparatus to which the embodiment of the present disclosure isapplied.

The residual data decoding unit 1430 reconstructs the residual block byperforming the same process as the residual data decoding unit 430 ofthe encoding apparatus according to the embodiment of the presentdisclosure.

The prediction unit 1440 generates a prediction block by performing thesame process as the prediction unit 410 of the encoding apparatusaccording to the embodiment of the present disclosure.

A reconstructed current block is generated by combing the residual blockreconstructed through the decoding unit 1430 and the prediction blockpredicted through the prediction unit 1440.

The deblocking filter unit 1450 filters the reconstructed current blockby performing the same process as the deblocking filter unit 460 of theencoding apparatus according to the embodiment of the presentdisclosure. Since the configuration of the deblocking filter unit 1450is substantially identical to the configuration of the deblocking filterunit 460 of the encoding apparatus, a detailed description thereof willbe omitted.

When utilizing the embodiment of the present disclosure, the deblockingmethod applied to the luma signal and the deblocking method applied tothe chroma signal can be equally implemented. In another embodiment, inits application, the deblocking method for application to the lumasignal and the deblocking method for application to the chroma signalcan be differently implemented.

It has been described in the above embodiments of the present disclosurethat the deblocking filtering is performed based on two neighboringblocks, the present disclosure is not limited thereto. That is, indefining the filtering strength and target pixels for performing thedeblocking filtering, two or more blocks may be involved, and it shouldbe construed that this also falls within the spirit of the presentdisclosure, without departing from the scope of the present disclosure.

In the description above, although all of the components of theembodiments of the present disclosure may have been explained asassembled or operatively connected as a unit, the present disclosure isnot intended to limit itself to such embodiments. Rather, within theobjective scope of the present disclosure, the respective components maybe selectively and operatively combined in any numbers. Every one of thecomponents may be also implemented by itself in hardware while therespective ones can be combined in part or as a whole selectively andimplemented in a computer program having program modules for executingfunctions of the hardware equivalents. Codes or code segments toconstitute such a program may be easily deduced by a person skilled inthe art. The computer program may be stored in computer readable media,which in operation can realize the embodiments of the presentdisclosure. The computer readable media may include magnetic recordingmedia, optical recording media, and carrier wave media.

In addition, terms like ‘include’, ‘comprise’, and ‘have’ should beinterpreted in default as inclusive or open rather than exclusive orclosed unless expressly defined to the contrary. All the terms that aretechnical, scientific or otherwise agree with the meanings as understoodby a person skilled in the art unless defined to the contrary. Commonterms as found in dictionaries should be interpreted in the context ofthe related technical writings not too ideally or impractically unlessthe present disclosure expressly defines them so.

Although exemplary embodiments of the present disclosure have beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from essential characteristics of thedisclosure. Therefore, exemplary embodiments of the present disclosurehave not been described for limiting purposes. Accordingly, the scope ofthe disclosure is not to be limited by the above embodiments but by theclaims and the equivalents thereof.

INDUSTRIAL APPLICABILITY

As described above, the present disclosure is highly useful forapplication in the fields of deblocking filtering and video encoding anddecoding. A subjective video quality and encoding efficiency can beimproved by reducing blocking artifact of an intra prediction block.

The invention claimed is:
 1. A decoding method for decoding a videosignal, comprising: decoding a residual block by performing inversequantizing and inverse transforming; generating a prediction block;reconstructing pixels of a reconstructed block by adding the predictionblock and the residual block; and performing deblocking filtering on ablock edge corresponding to the reconstructed block, based on whetherthe block edge corresponds to an edge between prediction blocks as wellas whether the block edge corresponds to an edge between transformblocks, wherein the deblocking filtering is performed by using at leastone of a first filtering mode which corresponds to a first filteringstrength and updates six pixels adjacent to the block edge; and a secondfiltering mode which corresponds to a second filtering strength andupdates four or fewer pixels adjacent to the block edge, the firstfiltering strength is stronger than the second filtering strength,wherein the second filtering mode calculates a delta value by using afirst difference between a first most neighboring pixel to the blockedge and a second most neighboring pixel to the block edge, a seconddifference between two pixels which are adjacent to the first mostneighboring pixel and a second most neighboring pixel respectively andhave the same distance from the block edge and an offset value, andupdates the first most neighboring pixel and the second most neighboringpixel by using the delta value, wherein an absolute value of acoefficient value corresponding to the second difference is larger than1/16 and smaller than the offset value, wherein the deblocking filteringdetermines the number of filtering target pixels based on apredetermined criteria, and the number of the filtering target pixelsincluded in a first block corresponding to the block edge is differentfrom the number of the filtering target pixels included in a secondblock corresponding to the block edge.
 2. The decoding method of claim1, wherein the transform block is able to have a size which exceed thesize of the prediction block.
 3. The deblocking method of claim 1,wherein the first filtering mode updates each of the first mostneighboring pixel and the second most neighboring pixel by using 5-tapfiltering corresponding to five pixels adjacent to the block edge.